1. Field of the Invention
The present invention relates to electrical circuits. More specifically, the present invention relates systems and methods for coupling electrical signals and current between objects that move relative to one other.
2. Description of the Related Art
In many devices, electrical signals are coupled between rotating objects, or between objects that move relative to one another. A classic example is the commutator and brush arrangement used in electric motors and generators. Typically, the commutator is formed as plural conductive cylindrical rings insulatively supported about an armature shaft that rotates together with armature windings. The commutator rings are electrically coupled to the armature windings. The brushes are held in a fixed position relative to the motor frame, or stator windings, and are typically urged toward the commutator rings by spring force. The brushes rotatably engage the commutator rings so as to enable the flow of electric current between the fixed position brushes and the rotating commutator rings, which couple the current to the armature windings. Depending on the type of motor or generator involved, the brushes may be electrically coupled to the stator or field windings or the brushes may be coupled to an external circuit, such as a power supply.
Of course, those skilled in the art will appreciate that there are a great variety of systems and circuits that require the coupling of electric current, or electrical signals, between movably related objects. The relative movement between objects is frequently rotational, however, linear and other non-linear relative movements are also encountered from time to time. Consider the amusement park bumper car. The floor area is at a first electrical potential and the ceiling area is at another potential. A first xe2x80x9cbrushxe2x80x9d engages the floor surface and second xe2x80x9cbrushxe2x80x9d is coupled to a pole and extends upwardly to engage the ceiling surface. Since the floor and ceiling are at different electrical potentials, the bumper car is enabled to draw electric current to operate its lights and motor. The motion of the bumper car is constrained within a plane parallel to the floor, but is otherwise random in nature. Of course, there are numerous other examples of considerably more sophisticated systems that require the moveable coupling of electric current and signals between objects.
An example of a sophisticated system that utilizes the moveable coupling of is electric signals is the airborne radar system deployed in various aircraft. For example, an F-15 fighter aircraft employs a tactical radar system deployed within its nose cone. The radar comprises a phased array antenna that forms a narrow radio beam in both of the transmit and receive modes of operation. In order to enable wide-angle radar coverage, the radar antenna is mounted on gimbals that enable the antenna, and therefore the radar beam, to be mechanically steered by servo-actuators. To enable the coupling of electric signals and power between the moveable antenna and other circuits fixed relative to the F-15 airframe, an electromechanical contact arrangement is employed. In many ways, this contact arrangement is not unlike the classic commutator and brush arrangements discussed above. Basically, two solid conductors are held in physical contact as they move relative to one another so as to maintain electrical continuity therebetween.
There are a number of problems associated with the conventional electromechanical coupling of signals through a commutator and brush arrangement. The effect of the brush dragging on the commutator causes friction. The friction produces heat and causes wear of the brush and commutator surfaces. The heat changes the electrical characteristic of the coupling, in particular altering the resistivity of the coupling. The wear implies that maintenance will ultimately be required. The electromechanical coupling is not perfect and thus is a source of electrical noise during operation. The noise results from variations in the quality of the signaling coupling. In extreme cases, arcing and loss of signal coupling can occur. Noise problems tend to increase as the mechanical components wear. This noise degrades the signal to noise ratio of the coupled signal, and can interfere with reliable operation. The noise created by electromechanical couplings can also radiate to interfere with other devices. In some circumstances, the noise power bandwidth may interfere with radio frequency devices causing other system""s reliability of be reduced.
Thus there is a need in the art for an apparatus for transferring electrical signals and electrical power between objects moveably related to one another, which improves reliability, reduces noise, minimizes coupling resistance, and allows flexible application in a variety of technologies.
The need in the art is addressed by the electrical joint of the present invention. The inventive electrical joint includes a first object that is moveably aligned with a second object. A conductive slurry is deposited upon a first surface of the first object, and a conductor is coupled to the second object and is aligned to maintain conductive coupling with the conductive slurry while the first object and the second object move relative to one other.
In a specific embodiment, the conductive slurry may comprise metallic particles suspended in a fluid. The metallic particles may be silver or copper. The first object may be formed from an insulator, such as polymide.
In a specific implementation of the foregoing invention, a non-conductive is disposed upon the exposed surface of the conductive slurry, and the conductor extends through the non-conductive gel to maintain the conductive coupling. The non-conductive gel may be hydraulic vacuum oil. In a further refinement, the conductive slurry is disposed within a channel of the first surface, and, the channel is positioned to maintain alignment with the conductor as the objects move relative to one another. The channel may be defined by a groove formed in the first surface or by built-up material extending from the first surface. The coupling of electrical signals is accomplished with a conductive coating disposed upon the first surface at a position to electrically couple the conductive slurry to the conductive coating. The conductive coating may be electroplated to the first surface.
In one embodiment, the first surface is substantially planar and the objects are constrained to move parallel to the first surface. In a second embodiment, the first object and the second object are moveably aligned about an axis or rotation, and, the first surface is cylindrical, having a centerline aligned with the axis of rotation. The conductor is a conductive blade that extends radially from the second object to maintain conductive coupling with the conductive slurry as the first object and the second object rotate with respect to one another. The blade may be a conductive disk. In a third embodiment, the first surface is planar and the second object is moveably aligned to rotate about an centerline extending perpendicular from the first surface, and the conductive slurry is disposed along a circular path defined by the movement of the conductor as the first object and the second object rotate with respect to one another. The conductor may be a conductive dowel extending from the second object to engage the circular path of conductive slurry. To improve reliability, the conductor may include a plurality of dowels extending from the second object and located at positions about a circle such that all of the dowels engage the circular path of conductive slurry.